Uniformly-shaped particulate resins have been used for various purposes such as electrophotographic toner particles, spacer particles for use in liquid crystal panels, colored particles for use in electronic papers, and carriers of medical agents for use in drugs and medicines.
Specific examples of the method for producing such uniformly-shaped particulate resins include methods in which a particulate resin having a uniform particle diameter is produced by making a reaction in a liquid, such as soap-free polymerization methods. Soap-free polymerization methods generally have advantages such that a particulate resin having a relatively small particle diameter can be easily produced; the particle diameter distribution is sharp; and the particle form is nearly spherical. However, on the other side, soap-free polymerization methods have problems to be solved such that the production efficiency is bad because a solvent is removed from resin particles in a medium, which is typically water; it takes a long time for the polymerization process; and a long time and large amounts of water and energy are necessary for producing a particulate resin because it is necessary for the methods to perform various processes after the end of a solidification process, such as a process for separating the resultant particulate resin from the solvent used, and processes for repeatedly washing and drying the particulate resin, to produce the particulate resin.
In attempting to solve the problems mentioned above, one of the present inventors and other inventors propose a toner production method using an ejection granulation method in JP-2008-292976-A. Specifically, according to the toner production method, a toner is produced as follows. Namely, in a droplet ejecting unit to eject droplets of a toner composition liquid, which is a raw material of toner, a thin film, on which multiple nozzles are formed, is vibrated by an electromechanical converter serving as a vibration generator to periodically vibrate the thin film up and down. Thereby, the pressure in a chamber, which contains the toner composition liquid and which includes the thin film having the multiple nozzles as a constitutional member, is changed, resulting in ejection of droplets of the toner composition liquid from the nozzles to an air space below the nozzles in response to the periodical change of pressure. The thus ejected droplets of the toner composition liquid naturally fall through the air space and proceed in the same direction, thereby forming lines of droplets of the toner composition liquid. In this regard, the ejected droplets are reshaped so as to be spherical due to the difference in surface tension between the toner component liquid and air in the air space. The reshaped droplets are then dried, resulting in formation of a particulate toner.
In addition, one of the present inventors and other inventors propose a toner production method in JP-2008-286947-A in attempting to prevent uniting of ejected droplets. Specifically, in this second toner production method, droplets of a toner composition liquid are ejected from multiple nozzles to continuously form droplets of the toner composition liquid. In addition, an airflow forming device is provided to supply an airflow in the droplet ejection direction through a narrow passage provided on a downstream side relative to the droplet ejection direction, so that the droplets are fed by the airflow and thereby uniting of the droplets is prevented.